s desired to descend.
Galion, of Avignon, wrote on aerostation in 1575; but the discovery of hydrogen made by Cavendish, in England, seemed to offer a feasible mode of accomplishing the object, and its use was suggested for that purpose by Dr. Black, in 1767, who ascertained that a light envelope filled with this gas would ascend.
The first machine by which an ascent was made into the upper regions of the atmosphere was invented and constructed by the brothers Stephen and Jscrewed for convenience of carrying in the pocket.
c. Gahn's blow-pipe made in four separable parts.
d. Wollaston's blow-pipe ready for use.
e. Wollaston's blow-pipe with its lower end and beak slid in for carriage in the pocket.
f. Dr. Black's blow-pipe.
The smaller end is the mouth-piece, and the larger condenses the moisture.
While the use of the blow-pipe dates from distant antiquity, yet its use in mineralogy, in determining the nature of the metals in ores, dates from Anto
condensed in filling it still exceeded the proportion of that required for large cylinders, according to the statements concerning them, given by Dr. Desaguliers.
He found, also, that all attempts to produce a better state of exhaustion, by throwing in more injection-water, occasioned a disproportionate waste of the steam.
Meditating on the cause of this, he attributed it to the fact that water boiled in vacuo at low heats (100° Fah.), — a discovery made by Dr. Cullen, the predecessor of Dr. Black in the University of Glasgow, — and he naturally inferred that at greater heats the water in the cylinder would produce a vapor which would partially resist the pressure of the atmosphere.
We now know that the vapor of water at 180° is equal to half the pressure of the atmosphere.
Watt made experiments on the power of steam by means of Papin's digester.
See also Muirhead's Mechanical inventions of James Watt, London, 1854.
Watt's single-acting steam-engine.
The single-acting s<